Gas turbines include components, such as buckets (blades), nozzles (vanes), combustors, shrouds, and other hot gas path components in which cracks and other undesirable features may form during formation or under operating conditions. Elimination of such cracks or other undesirable features may be inhibited by the materials from which the components are formed.
By way of example, certain gas turbine components include hard-to-weld (HTW) alloys due to desirable material properties, however, HTW alloys, due to their gamma prime and various geometric constraints, are susceptible to gamma prime strain aging, liquation and hot cracking, and are difficult to join when the gamma prime phase is present in volume fractions greater than about 30%, which may occur when aluminum or titanium content exceeds about 3%. As used herein, an “HTW alloy” is an alloy, which typically exhibits liquation, hot and strain-age cracking, and which is therefore impractical to weld in a repeatable manner without significant rework.
Additionally, even traditional brazing techniques may be difficult to apply to certain materials, such as directionally solidified and single crystal nickel-based superalloys due to the previously necessary inclusion of melting depressants in the braze materials to alloy brazing at temperatures, which do not induce recrystallization of the substrate. The inclusion of melting depressants is often undesirable due to the effects such melting depressants may have on the material characteristics of the substrate and the mechanical behavior of the brazed joint itself, as the melting depressants may lead to the formation of brittle phases. In order to dissolve such brittle phases, long dwell times at elevated temperatures (often above 800° C.) may be required to improve the mechanical performance of the joint to acceptable standards. Further, traditional brazing techniques may not adequately fill and seal cracks or other undesirably features. Narrow and branched cracks in particular may be difficult to be brazed in directionally solidified and single crystal substrates.